Safety primer for electric blasting caps



Oct. 27, 1942.

FIG. I

has

J. B. JOHNSON SAFETY PRIMER FOR ELECTRIC BLASTING CAPS Filed Dec. 1, 1938 2 Shets-Sheet 1 INVENTOR JOHN B. JOHNSON BY W 5. am-Q ATTORNEY Oct. 27, 1942. .1. B. JOHNSON 2,300,225

SAFETY PRIMER FOR ELECTRIC BLASTING CAPS Filed D sc. 1, 1938 2 Sheets-Sheet 2 FIG.6 FIG] INVENTOR JOHN B. JOHNSON ATTORNEY Patented John B. Johnson, Piedmont, Califl, assignor to Hercules Powder Company, Wilmington, DeL, a corporation of Delaware Application December 1, 1938, Serial No. 243,358

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4 Claims.

wires extending from the said bridge wire, said lead wires being held in place by a composition plug, waterproofing and a seal. The aforesaid lead wires extend beyond the cap a length convenient for connectionto an electrical circuit.

Electric blasting caps have been placed upon the market in many varying packaging styles that afford certain advantages during transportation and storage. Numerous styles of packages have claimed original safety features, which features hold only up to the tim the cap is to be red in the makeup of a primer or to the time the cap or primer is to be placed in the bore hole.

The term primer is used by those skilled in the art to denote any device for firing a definite quantity of explosive. majority of instances, normally means on of the two types of primers that the art regularly uses to initiate the detonation of an explosive charge. These two types of primers are first a primer consisting of a firing device, for example an electric blasting cap, or delay electric blasting, and second, a primer that is a prepared articie consisting of a cartridge of dynamite into which has been inserted a blasting cap. The article of thi invention which I have called a primer is an improved substitute for the primer defined above as consisting of a cartridge of dynamite into which has been inserted a blasting cap. Therefore, in this specification, although I shall necessarily use the term primer in reference to both the old and new article, it will be obvious to those skilled in the art whether I refer to the old dynamite cartridge-blasting cap primer, or to my new improved primer.

The safety of a blasting cap after it has been made into a primer, consisting of a blasting cap inserted into a dynamite cartridge, and after it has been used to prime a bore hole, is questionable, since during this period, from the makeup of the primer to the firing of th explosive charge,

the cap has no special protection against accidental blows, shock, or friction.

The object of this invention i to produce a primer that does not include a cartridge of dynamite, but contains a protected blasting cap, said ihe term, however in the primer being of such design and construction that it may be loaded directly into a bore hole thus alleviating the necessity and hazard of making up ordinary primers. Thus, my improved primer while ready for immediate use will furnish protection for the blasting cap from th time of manufacture to the actual time that the devic is fired by application of the firing current.

Now in accordance with this invention there has been produced an improved primer which is protected after manufacture at the factory, during transportation, storage, handling, loading operations, and also after being placed in the bore hole.

Having now indicated in a general way the nature and purpose of this invention there follows a more detailed description of preferred embodiments thereof with reference to the accompanying drawings in which,

Figure 1 is a plan view partly broken away of re primer embodying this invention.

Figure 2 is an end view of Figure 1.

Figure 3 is a view similar to Figure l, but differing from Figure 1 in the method of packaging the lead wires of the cap.

Figure 4 i an end View of Figure 3.

Figure 5 is a plan view partly broken away of a primer in accordance with thi invention that shows a variation of spool design and wiring packaging.

Figure 6 and Figure '7 are partial sectional views of spools used in this invention which have their ends countersunk and counterbored respectively.

Referring to the plan view Figure 1 and end view Figure 2, the device comprises a spool i provided with diametrically opposite slots 2 at each end which allows the lead wires 3, of a firing devic situated within a central longitudinal bore 5, after passing through a sulfur plug 6 to be positioned along the length of the spool I, across the end and through the slot 2 on the opposite side of the spool i, then said lead wires 3 are spirally wound about the spools l longitudinal axis and in a recess of suitable dimensions both as to length and depth thereof to accommodate varying lengths of lead wire.

Th spool I may be made of wood, fiber or other suitable material that does not readily transmit mechanical shock, and may be of the various shapes and designs that are found to be most convenient for any particular use. l'he central longitudinal bore 5 through the spool I is shown to be of two diameter thereby conforming to the design of the firing device 4 used. This bore may be of any size or shape but preferably of such design that the firing device 4 to be used will fit closely within the bore 5 and that the explosive end of the device 4 will be substantially flush with the end of the spool I. The lead wires 3 of the firing device 4 may be of varying lengths and for this reason the recess of the spool I may be of such dimensions that the lead wires 3 when wound spirally within thi recess will form a package of creditable appearance.

For tunnel and other work where normally the primers, consisting of a blasting cap inserted into a dynamite cartridge, are placed in or near the bottom of the bore hole there may be a staple I placed in the spool to hold the lead wires 3 in such a position that the natural way of loading my improved primer will be with the explosive end of the firing device 4 pointing towards the top of the hole and therefore into the main portion of the explosive charge.

sition with relation to the explosive charge may vary, care must; be exercised so to place the primer that the explosive end of the said primer is pointing into the major portion of the explosive charge thereby securing complete detonation of the entire charge.

The sulfur plug 6 is used in conjunction with the design of the central bore 5 to position the firing device 4 rigidly in such a manner that the explosive end of the firing device is substantially flush with the end of the spool I. This positioning may also be accomplished by using other suitable materials such as glue or pitch in place I of the sulfur plug 6.

A variation of my improved primer in regards to the method of packaging the lead wires is shown in side and end views by Figures 3 and 4 respectively. The primers of Figures 3 and 4 is substantially the device described in Figures 1 and 2 in that it comprises a spool I with a central longitudinal bore 5 containing a firing device i held in place by a sulfur plug 6. The lead wires 3 of this primer are packaged within a recess 8 of suitable dimensions both as to width and depth thereof to accommodate varying lengths of lead wires. This recess allows the lead wires 3 to be wound longitudinally about the spool I thus presenting a primer of varying appearance from the safety primer of Figures 1 and 2.

Figure 5 shows a further variation in the method of packaging the lead wires 3 of an improved primer. The lead wires 3 of this primer are folded, for example, in an accordion fold and positioned adjacent to the spool I. wires may be held in place by tape bands 9 or other suitable means. This device also differs from the preceding devices in that there is shown a firing device 4 which requires the central bore 5 to be straight or tapered in design to an extent that allows the explosive end of the firing device 4 to be substantially fiush with the end of the spool I.

Figure 6 shows a modification of the design of the spool I that includes countersinking II the central bore 5 of the spool I in such a manner that the firing device 4, while remaining substantially fiush with the end of the spool I, is exposed within the countersunk area II.

Figure 7 shows a modification of the design of the spool I similar to that shown in Figure 6 except that the central bore 5 of the spool I is counterbored I0 instead of countersunk.

The countersinking or counterboring of the If my improved primers are to be used in places where their 110-.

The folded lead central bore of the spool of this invention provides means whereby the dynamite used in conjunction with my improved primer will contact a larger area of the section of the cap containing the detonating charge. The countersinking or counterboring of the central bore of the spool while not essential is desirable as a construction which affords this additional contact between cap and dynamite will give more positive detonation of the explosive charge. The countersunk or counterbored area may be of sufiicient depth to expose the entire explosive section of the cap, but I prefer to countersink or counterbore the spool to a depth within a range equal to about half the height of the detonating charge contained with the cap. Thus, upon tamping dynamite into a bore hole containing one of my improved primers that has been countersunk or counterbored, ex-- cellent contact is obtained between the blasting cap of the primer and the dynamite and positive detonation is insured.

In accordance with this invention, the preferable method of holding the firing device rigidly in place within the central bore of the spool is described as a sulphur plug positioned above the firing device, but we may also position the firing device rigidly by other means examples of which are as follows: By wedging of said firing device in place; by using acentral bore of proper di mensions; by the use of an adhesive or plastic between the firing device and the walls of the central bore; by substitution of suitable compounds for sulfur in the plug method described; or by other suitable means of fastening the firing device rigidly into its proper place.

It is to be understood that primers in accordance with this invention may be of varying designs, therefore, I do not limit my invention to the shapes and designs described hereinbefore, but contemplate other desirable designs that may suggest themselves to those skilled in the art.

In the foregoing description the position of the explosive end of the firing device has been disclosed as being substantially flush with the end of the spool. This position of the explosive charge has been found to be the most efiicient location to assure the positive firing of the bore hole charge. Therefore the design of the central bore of the spool and the methods of rigidly fastening the firing device within said central bore must be so controlled as to produce a safety primer with the explosive end of the firing device and the end of the spool substantially flush. The explosive end of said firing device should not protrude from the spool to any appreciable extent, and preferably the end of the firing device will be flush with or slightly above the end of the said spool.

My improved primer as described fully protects from physical contact the blasting cap in the assembly. This said blasting cap will be protected at all times since it is in accordance with this invention as aforementioned to load the entire primer into the bore hole. The firing or detonation of the explosive charge will be positive as the primer is to be loaded into the bore hole with the end of the cap containing the detonating charge pointing at and in contact with the major portion of said explosive charge.

The advantage of my improved primer in tunnel work is of major importance as in some districts blasting caps and dynamite are not permitted to be transported into the tunnel together. This ruling precludes the possibility of transporting the normal blasting cap-dynamite cartridge, primers, known to the art into the tun-- nel. Therefore, it is necessary for operators to carry blasting caps to the face of a tunnel then bring dynamite to the face and prepare the blasting cap-dynamite cartridge primers while underground. This primer preparation is a dangerous occupation and could best be done above ground and in the open. The use of the improved primer of this invention alleviates the necessity of this dangerous occupation, as my primers when brought to the tunnel face are not to be inserted into a stick of dynamite but are ready to be loaded directly into a bore hole.

Although my primers are especially advantageous in tunnel work, their use will also be found advantageous in any explosive work where the necessity of preparing primers from a blasting cap and cartridge of dynamite is a prerequisite to blasting.

The improved primers of this invention have dealt with the use of electric blasting caps, but it is to be understood that in accordance with this invention primers may be prepared containing any firing device suitable for firing or detonating any commercial explosive. Thus my primers may be assembled which contain electric blasting caps, delay electric blasting caps, electric igniters, electric squibs, or other firing devices suitable for particular uses in the explosive industry.

It will be understood that the details and examples given hereinbefore are illustrative only, and in no Way limiting on invention as broadly described hereinbefore and in the appended claims.

What I claim and desire to protect by Letters Patent is:

1. In a prepared primer adaptable for direct loading into the bottom of a bore hole to effect detonation of an explosive charge the combination of a wooden spool, a longitudinal bore therethrough, an electric blasting cap disposed within said bore and integrally bonded to the Walls thereof, the detonating end of said cap substantially flush with one end of said bore and the lead wires of said cap extending from the other end of said bore, and back to the detonating end by means of a slot on the outer surface of said spool.

2. In a prepared primer adaptable for direct loading into the bottom of a bore hole to efifect detonation of an explosive charge the combination of a non-explosive, shock-resistant spool, a longitudinal bore therethrough, said bore flared inside near one end of said spool, an electric blasting cap of two different diameters disposed within said bore, and integrally bonded to the walls thereof, the detonating end of said cap substantially flush with the flared end of said bore and the lead Wires of said cap extending from the other end of said bore.

3. In a" prepared primer adaptable for direct loading into the bottom of a bore hole to eiTect detonation of an explosive charge placed above said primer the combination of a fiber spool, a longitudinal bore therethrough, said bore flared at one end, an electric blasting cap disposed within said bore and integrally bonded to the Walls thereof, the detonating end of said cap substantially flush with the flared end of said bore and the lead wires of said cap extending from the other end of said bore, passing in a slot on the outer surface of said spool back to the detonating end and then coiled about said spool.

4. A combined package and prepared primer adapted to be placed in a bore hole below and adjacent an explosive charge, comprising a spool having a longitudinal bore therethrough and a countersunk portion at one end of said bore, a blasting cap integrally secured in said longitudinal bore, a firing means attached to one end of said cap and passing outside said spool, said cap being positioned so as to protrude from said countersunk portion so as to intimately contact said explosive.

JOHN B. JOHNSON.

I CERTIFICATE OF CORRECTION.

Patent No. 2,500,225. October 27 19m.

JOHN B. JOHNSON.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 5, first column, line 59, and second column, line 8,, claims 1 and2, after the word "charge" insert placed above said primer,; and that the said Letters Patent should be read with this correction therein that the same may conform to the record of the case in the Patent Office. I

Signed and sealed this 29th day of December, A. D. 19Lr2.

Henry Van Arsdale, (Seal) Acting Commissioner of Patents.

- r CERTIFICATE OF CORRECTION. I Patent No. 2,500,225. October 27, 19L 2.

JOHN B. JOHNSON. t

It is hereby certified that error eppears in the printed specification of the above numbered patent requiring correction as follows: Page 5, first column, line 59, and second column, line 8,, claims 1 and 2, after the word "charge" insert --placed above said primer,-; end that the said Letters 1 l 1 Patent should be read with this correction therein that the same may conform to the record of the' case in the Patent Office Signet and sealed this 29th day of December, A. D. 19L 2.

Henry Van Arsdale, (Seal) Acting Commissioner of Patents. 

